Measuring Temp & Humidity in the Root Cellar

Now that the door is in place, we can see how well the root cellar in the shed is maintaining the desired temperature and humidity conditions.

I hacked together a quick temperature and humidity sensor (pictured left) that could log data records to an SD card (using the DHT22 sensor from Adafruit connected to an Arduino) and used it to collect data from approximately 7:30am CT yesterday through about 5:30 am today.

Here’s the data in the root cellar (pardon the ugly axis labels):

And here’s the same data from outside over the same time range (via weatherspark.com):At a glance, I think this is a good result. Both temp. and relative humidity were held much more stably in the cellar than outside. Temp stayed almost 10 degrees F below the outside temp, and humidity stayed high in the cellar when it dropped outside during the afternoon yesterday.

This needs further study, and in particular I’m concerned that the cellar is warmer than ideal right now, but I think we’re on the right track.

Actually, high humidity is a necessity for most food storage. High humidity is not good for explicitly dried things (e.g. beans), things that are dry-cured for storage (onion, garlic), or canned goods (which can rust), but most fresh fruits and vegetables want moderate to high-humidity. This chart has a good overview of the range.

As far as why it’s more humid in there, I think it’s the dirt floor and the relatively small, enclosed space.

So the humidity is what we were shooting for. The temp is another matter — it’s a bit too warm — and I’m particularly interested to see how it did when it briefly got really warm outside.